1. Field of the Invention
This invention relates to a method of and an apparatus for controlling a piezoelectric vibratory parts feeder which feeds various types of parts by vibration of a piezoelectric vibrating element.
2. Description of the Prior Art
A typical example of the conventional piezoelectric vibratory parts feeders comprises, as shown in FIG. 1, a bowl 2 adapted to accommodate therein a large number of parts for supply and discharge the parts while exerting vibration to the bowl, a vibrating unit 4 provided with a piezoelectric vibrating element for driving the bowl 2 at a predetermined resonance frequency, and a piezoelectric driving control system 5 for driving the vibrating unit 4. This piezoelectric vibratory parts feeder is adapted to electrically detect a vibration amplitude of the bowl 2 by an amplitude sensors 6 such as, for example, a photoelectric transducer and a piezoelectric element, feed it back to the piezoelectric driving control system 5, and control the electric current or voltage for driving the bowl 2 to drive the bowl at a constant amplitude at any time.
Since this method requires the amplitude sensor 6 to detect the vibration of the bowl 2, the construction of the system becomes complicated, the number of components increases, and also the cost becomes high.
Another system is proposed, as disclosed in Japanese Patent Applications, KOKAI (Early Publication) No. JP,7-60187,A and No. JP,10-49237,A, to perform predetermined operation or processing based on a signal obtained from an electric current detector or a voltage detector connected to a driving circuit, thereby controlling the driving signal of the driving circuit of a piezoelectric vibrating element without using a special amplitude sensor.
Although it is not necessary to provide a special amplitude sensor in the case of this method, it requires controlling of additional operation, processing, etc. in order to detect the current value or the like at the time of driving thereby controlling the vibration of the vibrating unit 4. Consequently, a control system becomes complicated with size of the apparatus increased, and also the cost becomes high.
An object of the present invention is, therefore, to provide a method of and an apparatus for controlling a piezoelectric vibratory parts feeder with simple construction and enabling accurate vibration.
In accordance with one aspect of the present invention, there is provided a method of controlling a piezoelectric vibratory parts feeder which comprises a piezoelectric vibrating unit provided with a piezoelectric vibrating element that vibrates at a predetermined frequency, a bowl adapted to discharge parts accommodated therein by means of the piezoelectric vibrating unit, a driving circuit for driving the piezoelectric vibrating element, and a control unit for outputting a driving signal to the driving circuit to cause a predetermined driving. The method comprises idling the driving of the piezoelectric vibrating element temporarily at every predetermined driving cycles of the piezoelectric vibrating element and controlling vibration of the piezoelectric vibrating element based on a signal obtained from the piezoelectric vibrating element mentioned above by its piezoelectric effect during the idling period, for instance, based on a phase difference between a waveform of this signal and the driving signal of the driving circuit mentioned above.
In a preferred embodiment, a resonance frequency of the piezoelectric vibratory parts feeder is previously measured before it is controlled. When the measurement of the resonance frequency is made, the piezoelectric vibrating element is driven by the driving circuit mentioned above, the driving by the driving circuit is temporarily idled at every predetermined driving cycles, and the signal obtained from the piezoelectric vibrating element by its piezoelectric effect is measured during the idling period. The frequency at which the signal becomes maximum is assumed as a resonance frequency. Then, the piezoelectric vibrating element is driven by the driving circuit at the obtained resonance frequency, and the driving by the driving circuit is temporarily idled at every predetermined driving cycles. During the idling period, a signal obtained from the piezoelectric vibrating element by its piezoelectric effect, a phase difference between a waveform of this signal and the driving signal of the driving circuit mentioned above, and the resonance frequency mentioned above are stored in a storage element. When the piezoelectric vibrating unit is driven, it is driven at the resonance frequency stored. Furthermore, the control of the piezoelectric vibrating element is carried out in such a way that the phase difference between the waveform of the signal obtained by the piezoelectric effect and the driving signal of the driving circuit becomes equal to the stored phase difference mentioned above.
In accordance with a second aspect of the present invention, there is provided a system for controlling a piezoelectric vibratory parts feeder. This system comprises a piezoelectric vibrating unit provided with a piezoelectric vibrating element that vibrates at a predetermined frequency, a bowl adapted to discharge parts accommodated therein by means of the piezoelectric vibrating unit, a driving circuit for driving the piezoelectric vibrating element, a control unit for outputting a driving signal to the driving circuit to cause a predetermined driving and temporarily idling the driving of the piezoelectric vibrating element at every predetermined driving cycles of the piezoelectric vibrating element, a signal detecting means for detecting a waveform of a signal obtained from the piezoelectric vibrating element by its piezoelectric effect during the idling period, a phase difference detecting means for detecting a phase difference between the waveform of the signal obtained by the signal detecting means and the driving signal waveform of the driving circuit, and a vibration controlling means for controlling vibration of the piezoelectric vibrating element based on the phase difference obtained by the phase difference detecting means.
In this specification, the signal mentioned above indicates a voltage or an electric current. When the signal indicates a voltage, the term xe2x80x9csignalxe2x80x9d involves a voltage waveform, a driving voltage, a voltage detecting means, and a driving voltage waveform. When the signal is an electric current, it involves a current waveform, a driving current, a current detecting means, and a driving current waveform.
The method of and the apparatus for controlling the piezoelectric vibratory parts feeder as constructed above are capable of accurately detecting the vibration by utilizing the piezoelectric vibrating element itself as a sensor, without using a special amplitude sensor that detects the amplitude of the piezoelectric vibrating unit, so that the construction thereof can be remarkably simplified. Moreover, since the resonance frequency of the parts feeder is once measured and stored and the parts feeder is operated based on the stored resonance frequency and other signals or the data of phase difference, it is possible to drive the parts feeders on their respective optimal driving conditions. Since the resonance frequency can be measured again even when the construction of the parts feeder is changed, it is possible to drive the parts feeder always at suitable conditions.